1. Field of the Invention
The present invention relates to a fixing device that heats and melts toner adhering to paper in order to fix the toner thereto and form an image.
2. Description of the Related Art
In a conventional thermal fixing device of a laser beam printer, a hollow cylindrical drum, made of aluminum and covered by heat-resistant rubber, is used as a fixing drum, and a halogen heater is disposed inside the drum to heat the fixing drum.
The halogen heater is provided with a supporting member and a power feeding member, separately. The halogen heater is supported on the frame using the supporting member, while electric power is supplied to the halogen heater using the power feeding member through a flexible lead wire extending from the halogen heater. In the fixing device structured as described above, a power feeding member and a heater supporting member must be provided and assembled. Accordingly, the number of components as well as the number of assembling steps are increased and productivity is reduced. Another problem is that the halogen heater is pressed against the frame and secured directly thereto, which may cause the halogen heater to break.
To address the forgoing problems, Japanese Laid-Open Patent Publication No. 8-44233 discloses a fixing device in which a heater, which has, at its opposite ends, high rigidity pin-shaped terminals, is used to allow support of the heater as well as power supply to the heater. In such a heater, if the terminals at the opposite ends are supported while power is supplied thereto, a heater tube can be supported and supplied with power at the same time.
FIG. 12 shows the heater disclosed in the above publication. As shown in FIG. 12, a power feeding member of the heater is a thin metal plate 101, bent into a U-shape, that holds a terminal 104 of a heater tube 103 disposed along a central axis of a fixing roller 102. A power feeding terminal 105 is laminated with the thin metal plate 101, and the power feeding terminal 105 and the thin metal plate 101 are secured to the frame 107 by a screw 106.
The halogen heater heats up to high temperatures quickly when supplied with electric power. Quartz glass surrounding the periphery of the halogen heater has a lower linear thermal expansion coefficient than usual alkaline line glass, and a high stability against drastic temperature changes. However, quartz glass is low in mechanical strength and susceptible to mechanical shock and strain. Therefore, when the terminal 104 of the halogen heater is directly secured to the power feeding terminal 105 of the frame 107, as disclosed in the above publication, the heater is apt to be broken due to mechanical strain caused by the difference in thermal expansion coefficient between the heater and the frame.
In another fixing device, a terminal of a heater is held by a power feeding terminal urged by a spring. In this case, the spring urging force is changed due to the difference in thermal expansion coefficient between the heater and the frame, and electric contact becomes unstable.
In still another fixing device, contact surfaces of a terminal of a heater and a terminal supporting member are made smooth, and the terminal is screw-held to the supporting member slidably under a predetermined pressure. However, polishing and smoothing is difficult. In addition, the terminal of the heater is usually made of tungsten, while the terminal supporting member, that is, an electrode, is made of phosphor bronze based upon this material's resilience and conductivity. The difference in hardness of the metals might cause biting and make sliding impossible.